Optical articles, that is devices for aiding vision, whether through image magnification, image intensification, or vision correction, are well known. Examples of such articles include camera lenses, binocular and telescope lenses, spectacle lenses, intraocular lenses, contact lenses, and lenses used in corneal transplants and implants.
Glass was the earliest material used to make such devices. However, glass has been replaced by polymeric materials as the material of choice in many such devices.
Often polymeric optical devices are made from reactive organic precursors by reacting (e.g., polymerizing, vulcanizing, etc.) one or more components in a mold. Examples of such processes are disclosed in U.S. Pat. Nos. 4,121,896 and 4,208,364 which are directed to a mold device and a method of using that device, and in U.S. Pat. No. 4,469,646 which is directed to another molding method. These processes are illustrative of the techniques employed to manufacture vision correcting lenses such as contact lenses by molding techniques.
These molding processes suffer from the disadvantage that the mold halves employed are often not properly aligned with one another (i.e., their principal longitudinal axes are not in coincident alignment) so that the resultant lenses are toric, i.e., they contain cylinder and prism defects. This occurs because the mold members are generally placed together by hand and then, optionally, pressed together. However, pressing the mold halves together in this fashion often fails to properly align the mold halves. Accordingly, great care must be taken when placing the mold halves together.